This invention relates to the non-destructive measurement of the thermal time constant of fine metal wire segments, especially wire segments of the type used to initiate explosive reactions.
Many explosive and pyrotechnic devices are detonated by the heat generated when a large electrical signal is passed through a metal wire segment embedded in the device. The non-destructive testing of these wire segments is important to ensure the continued reliability and readiness of devices already built and to confirm that wire segments yet to be installed are capable of accomplishing their task.
The prior art technique for the non-destructive testing of the thermal time-constant of fine (i.e. small, thin) wires, first developed in 1959, is carried out with a testing apparatus that includes a constant-current source which is switched on suddenly to pass a small current through the wire (a current of such small magnitude that it would not destroy the wire or generate sufficient heat to detonate the device), and then recording the voltage developed across the wire as a function of time. The data recorded is then compared with an exponential curve to provide some indication of the thermal time constant of the wire under test. Unfortunately, this method is cumbersome, it ought to be performed by a skilled operator, and it gives results of inconsistent validity.
Accordingly, there remains a need for a simple and reliable method and apparatus for testing fine wire segments.